1. Field of the Invention
This invention relates to an electronic musical instrument and more particularly to a novel musical wave generator which generates plural waves having different frequencies using interpolation calculation of wave sample data.
2. Description of the Prior Art
A conventional wave generator for an electronic musical instrument utilizing digital systems has a digtial memory storing samples of a complex wave shape of a musical tone. The samples in the memory are read out by a clock pulse and converted to analog signals. The analog signals have the shape of the musical tone. The analog signals are multiplied by an envelope signal. Such systems have several problems.
The first problem is wave calcuation. Timbre of musical tone is determined by level of harmonics. A complex wave shape of the tone can be calculated by inverse Fourier calculation of the level data. When the level data are changed from one timbre to another, the inverse Fourier calculation must be executed. This calculation takes too much time. So, an electronic musical instrument cannot produce a new timbre immediately after a timbre switch is operated.
The second problem is that timbre does not change during onset and end of the tone. To change the timbre, the inverse Fourier calculation must be done all the time, but speed of the calculation is not fast enough, so this is impractical. Therefore, good sounds having realistic image of a trumpet or a violin cannot be generated.
The third problem concerns clock signal frequency. For generating musical scales C, C.music-sharp., D, . . . . , B, twelve clock frequencies are prepared and one of them is used as clock signal frequency. This method is convenient for monophonic musical instruments, but not for polyphonic musical instruments. When C and C.music-sharp. should be generated, these two frequencies are different from each other, so a single clock frequency system cannot be adopted. The system becomes too complicated, because synchronizing two frequencies of C and C.music-sharp. is necessary.
The fourth problem is that it is hard to obtain frequency resolved precisely at will unless very large memory is prepared.